Check valves are conventionally used in applications where it is desirable to allow a flow of fluid in one direction and to prevent flow in the reverse or “backflow” direction. For instance, a check valve assembly can be used to prevent the backflow of used or dirty oil from a fryer or filter station in an oil handling system to avoid the risk of contaminating fresh or clean oil and incurring potential health hazards.
To achieve this function, check valve assemblies typically have a movable check member which is seated against a valve seat in a valve inlet passage and/or a valve outlet passage when the check member is in a closed or shunted position. When the check member is unseated from the respective inlet or outlet passage seat, the check member is opened and a “forward” flow can be introduced into and through the valve.
A check member disposed in the valve inlet passage is typically constructed so that it is unseated only in response to a sufficient opening or “cracking” fluid pressure on an upstream side of the inlet passage. In contrast, a backflow on a downstream side of the inlet passage is ineffective to unseat the inlet check member and open the valve. Similarly, an outlet check member is constructed so that it is unseated only in response to sufficient opening or cracking fluid pressure on an upstream side of the outlet passage, whereby a backflow on a downstream side of the outlet passage is ineffective to unseat the outlet check member and open the valve. Generally, the requisite fluid pressure needed to open or crack a check member must be greater than a biasing closing pressure exerted by a resilient member engaged on a backside of the check member.